Every year, Ford changed the design of underdash harnesses,
often times within each model year! Here's a quick guide for
identifying each vintage Mustang underdash Harness. We have
highlighted only those unique features for each model year. Assume
that the design carries on for the following year until a change is noted.

1970: Similar to 1969, except igniton switch now 6 of 8 pin
parallel gray connector. Gauge harness extends all the way to the
battery and alternator (unique to this year).

1971: Similar to 1969 and 1970, but ignition is now black
with red stripe on connector face. Gauge harness has plugs beyond
firewall. Tach version has 12 pin dash connector instead of 18 pins.
Red molded plug going to rear has 3 of 4 pins used.

1972: Similar to 1971. Near right side, a red plastic
plug has 4 of 6 pins used. Tach version has 12 pin dash connector
instead of 18 pins. Red molded plug going to rear has 3 of 4 pins
used.

1973. Similar to 1972, but turn signal connector is
now heavy duty. Tach version has 12 pin dash connector instead of 18
pins. Red molded plug going to rear has 2 of three pins used.